DAVOS, Switzerland — Trade ministers from many of the world’s biggest economies pledged to broaden a deal to boost global trade Saturday, with the U.S. saying nothing is off-limits for discussion.

At a Swiss-hosted meeting on the sidelines of the World Economic Forum, ministers from China, the European Union, Japan, the U.S. and 15 other nations agreed to build on the “positive momentum” of a World Trade Organization summit last December in Bali where the organization’s 159 member economies agreed to cut customs red tape.

The ministers agreed to address the most difficult remaining negotiating topics of agriculture, market access and services that eluded an agreement last month in the first WTO deal since the global trade body was formed in 1995, said Swiss Economics Minister Johann Schneider-Ammann, who hosted the meeting.

He said the world economic powers agreed to “promptly” build on the Bali agreement with “a particular focus on issues important to least developing countries.”

“In order to be able to successfully tackle these topics, fresh and credible approaches will be needed,” the Swiss minister said.

WTO Director-General Robert Azevedo said negotiating process must be transparent and inclusive, so every member can have a voice and participate, but that “the do-ability test is very important” in working toward an expanded free-trade deal that balances “ambition and realism.”

The Bali deal could boost global trade by $1 trillion over time, and its centerpiece was an agreement on measures to ease barriers to trade by simplifying customs procedures and making them more transparent.

But it also kept alive hopes of eventually accomplishing the WTO’s broader Doha Round of trade negotiations, sometimes known as the development round because of sweeping changes in regulations, taxes and subsidies that would benefit low income countries.

And the deal boosted the Geneva-based WTO’s credibility and relevance as a forum for governments to negotiate trade agreements and not just as a trade court for international disputes.

U.S. Trade Representative Michael Froman told ministers Saturday that “the WTO’s first order of business must be to finish what we started,” according to a statement from his office.

“It also means agreeing to a work plan as we seek to identify future opportunities for progress,” he told them. “The United States is open-minded and we are willing to consider a discussion on any of the outstanding issues.”

Japanese Economics Minister Toshimitsu Metegi said Saturday’s discussion focused on “how to go forward with the WTO” while also implementing the red tape-cutting provisions previously agreed to in Bali. Japan, he told reporters, has shown “a considerable amount of flexibility” during the trade talks and hopes the U.S. will be similarly flexible at the negotiating table.

The world’s biggest powers in trade have also vowed to craft a global deal on free trade in environmental goods to help fight global warming.

U.S., EU, Chinese and Japanese trade ministers were among the group of developed economies that announced the effort a day earlier. Their statement said the economies would focus on green products, technologies and services that the WTO estimates to be worth $1.4 trillion.